You'll need to be able to boot the Windows 7 DVD to access it's Repair console on second screen to run the Repairs. Windows 7's failure to start should not in any way affect your ability to boot the DVD.
Set DVD drive as first device to boot in BIOS setup: How to Boot your Computer from a Bootable CD or DVD
If that fails, try using the one-time BIOS boot menu key which every computer and mobo has.
You may need to burn a System Repair CD from the link I posted earlier. Or tap the F8 key at bootup to see if the Repair console is on your Advanced Boot Options: System Recovery Options
Fill in your System Specs so we can help you better.